Networked virtual environments allow users at remote locations to use a telecommunication link to coordinate work and social interaction. Teleconferencing systems and virtual environments that use 3D computer graphic displays and digital video recording systems allow remote users to interact with each other, to view virtual work objects such as text, engineering models, medical models, play environments and other forms of digital data, and to view each other's physical environment.
A number of teleconferencing technologies support collaborative virtual environments which allow interaction between individuals in local and remote sites. For example, video-teleconferencing systems use simple video screens and wide screen displays to allow interaction between individuals in local and remote sites. However, wide screen displays are disadvantageous because virtual 3D objects presented on the screen are not blended into the environment of the room of the users. In such an environment, local users cannot have a virtual object between them. This problem applies to representation of remote users as well. The location of the remote participants cannot be anywhere in the room or the space around the user, but is restricted to the screen.
Head-mounted displays (HMDs) have been widely used for 3D visualization tasks such as surgical planning, medical training, or engineering design. The main issues of the conventional eyepiece-based HMD technology include tradeoffs between resolution and field-of-view (FOV), and between compactness and eye clearance, the presence of large distortion for wide FOV designs, the conflict of accommodation and convergence, the occlusion contradiction between virtual and real objects, the challenge of highly precise registration, and often the brightness conflict with bright background illumination. The concept of head-mounted projective displays (HMPDs) is an emerging technology that can be thought to lie on the boundary of conventional HMDs, and projective displays such as the CAVE technology.
The basic HMPD concept of projection head-mounted display was early disclosed by Fisher Nov. 5, 1996, in U.S. Pat. No. 5,572,229.
Also a first international presentation was done by Kijima and Ojika in 1997 [See Kijima and Ojika, “Transition between virtual environment and workstation environment with projective head-mounted display.” Proceedings of IEEE 1997 Virtual Reality Annual International Symposium, IEEE Computer Soc. Press. 1997, pp. 130–7. Los Alamitos, Calif., USA.].
Also on Apr. 15, 1997, a U.S. Pat. No. 5,621,572 was also issued to Ferguson on the conceptual idea of a display, i.e. optical, system for head mounted display using phase conjugate material and method of displaying an image. Independently, the technology of HPMD was developed by Parsons and Rolland as a tool for medical visualization [See Parsons and Rolland, “A non-intrusive display technique for providing real-time data within a surgeon's critical area of interest. “Proceedings of Medicine Meets Virtual Reality 98, 1998, pp. 246–251”]. After the initial proof of concept using off-the-shelf components, a first-generation custom-designed HMPD prototype was built to investigate perception issues and quantify some of the properties and behaviors of phase conjugate materials in an imaging system. Since, the projection system of the first-generation prototype was custom designed using a double-Gauss lens structure and built from commercially available components. The total weight of each lens assembly was about 50 grams (already a significant reduction compared to using off-the-shelf optics) with mechanical dimensions of 35 mm in length by 43 mm in diameter.
Common to all these teleconferencing systems is the use of lenses of various configurations and weights with distortions, lack of clarity and smearing of the televised images. Representative of lenses that might at first glance appear to be useful in the teleconferencing systems are also shown in:                U.S. Pat. No. 5,526,183 by Chen who teaches the use of a lens combining diffractive elements of both glass and plastic to reduce the weight and size of the lens within a conventional helmet mounted display rather than the necessary projective helmet mounted display;        U.S. Pat. No. 5,173,272 by Aoki which discloses a four element high aperture lens with glass elements making it too heavy for helmet mounting;        U.S. Pat. No. 4,753,522 by Nishina et al which lens features all 4 plastic elements and is fully symmetrical which latter property is imposed by its restricted application—a copy machine lens; and,            U.S. Pat. No. 4,669,810 by Wood which shows a head-mounted display with many (more than 4) optical elements in the relay optics.
Consequently, there is a need for a HMPD augmented reality display that mitigates the above mentioned disadvantages and has the capability to display virtual objects and environments, superimposes virtual objects on the “real world” scenes, provides “face-to-face” recording and display, be used in various ambient lighting environments, and corrects for optical distortion, while minimizing weight, computational power and time. Lightweight, compactness, enhanced mobility and improved fidelity of the field of view are always of basic importance and/or highly desirable, particularly, for head-mounted devices.